1. Field
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays (FPDs), integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a complete multilayer device. This pattern can be transferred onto a substrate by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning means can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can comprise a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A typical substrate can be round a round silicon wafer or a rectangular glass plate. Typically lithographic imaging systems have insufficient field to expose the full area of a substrate. To overcome this limitation the substrate can be scanned underneath image field, while the mask or reticle is synchronously scanned through the illumination beam. In this way, the pattern is transferred to a larger area of the substrate. If the scanned exposure region covers the full width and length of the substrate then exposure can be completed with a single scan. Otherwise, the substrate is stepped either laterally or in the scan direction, and the exposure process repeated until the entire substrate is exposed.
Alternatively the moving reticle or mask can be replaced by a stationary mirror array where the pattern is electronically generated by moving the mirrors as the resist coated substrate is scanned.
In order to properly pattern the substrate, the resist needs to be in a focal plane of a projection system. This is typically achieved through use of combination of a complex multi-axis metrology measurement system that controls the motion of the substrate stage often in 6 degrees of freedom, and separate sensors that measure the location of the substrate surface. The metrology components used to measure substrate position in the direction orthogonal to the substrate plane are expensive, and may occupy volume, which conflicts with space needed for other tool components.
Therefore, what is needed is a system and method that accurately measure a surface of an object, while reducing a number and/or complexity of devices in the system.